1. Field of the Invention
The present invention relates to a digital data reproducing apparatus and, more particularly, to an apparatus for reproducing digital data from a recording medium using a rotary head.
2. Related Background Art
As a conventional apparatus of this type, a VTR for recording/reproducing an image signal and an audio signal on/from a magnetic tape using a rotary head is known.
In such a VTR, the recording/reproducing start position of the head is controlled with high precision using a head switch pulse (to be referred to as an SWP hereinafter) which indicates the positional relationship of the head with respect to the tape.
The SWP is normally generated using a PG signal indicating the rotation phase of a cylinder. In this case, the phase relationship between the head and the PG signal is determined by the mounting precision of a motor of the cylinder which mounts the head, and the cylinder, and varies in units of apparatuses. For this reason, since the phase difference between the PG signal and the SWP varies in units of apparatuses, an appropriate SWP is obtained by adjusting the phase difference between the PG signal and the SWP in units of apparatuses.
However, in the above-mentioned conventional apparatus, the phase adjustment of the SWP must be performed in each apparatus, resulting in a very cumbersome operations.
The phase adjustment of the SWP is normally performed by a specialist upon delivery from a factory. Thus, it is impossible to perform the phase adjustment when the phase of the SWP deviates from that upon delivery due to the poor mounting precision of the motor and the cylinder, deterioration of the motor performance, and the like after delivery of the apparatus to a user.
Furthermore, in a domestic-use VTR, the recording start positions of data in tracks on tapes do not always precisely match among cassettes, and the phase of the SWP may be proper in a given cassette but may be improper in another cassette.